path: root/ethchain/state_transition.go

package ethchain

import (
    "fmt"
    "math/big"

    "github.com/ethereum/go-ethereum/ethstate"
    "github.com/ethereum/go-ethereum/ethutil"
    "github.com/ethereum/go-ethereum/vm"
)

/*
 * The State transitioning model
 *
 * A state transition is a change made when a transaction is applied to the current world state
 * The state transitioning model does all all the necessary work to work out a valid new state root.
 * 1) Nonce handling
 * 2) Pre pay / buy gas of the coinbase (miner)
 * 3) Create a new state object if the recipient is \0*32
 * 4) Value transfer
 * == If contract creation ==
 * 4a) Attempt to run transaction data
 * 4b) If valid, use result as code for the new state object
 * == end ==
 * 5) Run Script section
 * 6) Derive new state root
 */
type StateTransition struct {
    coinbase, receiver []byte
    tx                 *Transaction
    gas, gasPrice      *big.Int
    value              *big.Int
    data               []byte
    state              *ethstate.State
    block              *Block

    cb, rec, sen *ethstate.StateObject
}

func NewStateTransition(coinbase *ethstate.StateObject, tx *Transaction, state *ethstate.State, block *Block) *StateTransition {
    return &StateTransition{coinbase.Address(), tx.Recipient, tx, new(big.Int), new(big.Int).Set(tx.GasPrice), tx.Value, tx.Data, state, block, coinbase, nil, nil}
}

func (self *StateTransition) Coinbase() *ethstate.StateObject {
    if self.cb != nil {
        return self.cb
    }

    self.cb = self.state.GetOrNewStateObject(self.coinbase)
    return self.cb
}
func (self *StateTransition) Sender() *ethstate.StateObject {
    if self.sen != nil {
        return self.sen
    }

    self.sen = self.state.GetOrNewStateObject(self.tx.Sender())

    return self.sen
}
func (self *StateTransition) Receiver() *ethstate.StateObject {
    if self.tx != nil && self.tx.CreatesContract() {
        return nil
    }

    if self.rec != nil {
        return self.rec
    }

    self.rec = self.state.GetOrNewStateObject(self.tx.Recipient)
    return self.rec
}

func (self *StateTransition) UseGas(amount *big.Int) error {
    if self.gas.Cmp(amount) < 0 {
        return OutOfGasError()
    }
    self.gas.Sub(self.gas, amount)

    return nil
}

func (self *StateTransition) AddGas(amount *big.Int) {
    self.gas.Add(self.gas, amount)
}

func (self *StateTransition) BuyGas() error {
    var err error

    sender := self.Sender()
    if sender.Balance().Cmp(self.tx.GasValue()) < 0 {
        return fmt.Errorf("Insufficient funds to pre-pay gas. Req %v, has %v", self.tx.GasValue(), sender.Balance())
    }

    coinbase := self.Coinbase()
    err = coinbase.BuyGas(self.tx.Gas, self.tx.GasPrice)
    if err != nil {
        return err
    }

    self.AddGas(self.tx.Gas)
    sender.SubAmount(self.tx.GasValue())

    return nil
}

func (self *StateTransition) RefundGas() {
    coinbase, sender := self.Coinbase(), self.Sender()
    coinbase.RefundGas(self.gas, self.tx.GasPrice)

    // Return remaining gas
    remaining := new(big.Int).Mul(self.gas, self.tx.GasPrice)
    sender.AddAmount(remaining)
}

func (self *StateTransition) preCheck() (err error) {
    var (
        tx     = self.tx
        sender = self.Sender()
    )

    // Make sure this transaction's nonce is correct
    if sender.Nonce != tx.Nonce {
        return NonceError(tx.Nonce, sender.Nonce)
    }

    // Pre-pay gas / Buy gas of the coinbase account
    if err = self.BuyGas(); err != nil {
        return err
    }

    return nil
}

func (self *StateTransition) TransitionState() (err error) {
    statelogger.Debugf("(~) %x\n", self.tx.Hash())

    // XXX Transactions after this point are considered valid.
    if err = self.preCheck(); err != nil {
        return
    }

    var (
        tx       = self.tx
        sender   = self.Sender()
        receiver *ethstate.StateObject
    )

    defer self.RefundGas()

    // Increment the nonce for the next transaction
    sender.Nonce += 1

    // Transaction gas
    if err = self.UseGas(vm.GasTx); err != nil {
        return
    }

    // Pay data gas
    dataPrice := big.NewInt(int64(len(self.data)))
    dataPrice.Mul(dataPrice, vm.GasData)
    if err = self.UseGas(dataPrice); err != nil {
        return
    }

    if sender.Balance().Cmp(self.value) < 0 {
        return fmt.Errorf("Insufficient funds to transfer value. Req %v, has %v", self.value, sender.Balance)
    }

    var snapshot *ethstate.State
    // If the receiver is nil it's a contract (\0*32).
    if tx.CreatesContract() {
        // Subtract the (irreversible) amount from the senders account
        sender.SubAmount(self.value)

        snapshot = self.state.Copy()

        // Create a new state object for the contract
        receiver = MakeContract(tx, self.state)
        self.rec = receiver
        if receiver == nil {
            return fmt.Errorf("Unable to create contract")
        }

        // Add the amount to receivers account which should conclude this transaction
        receiver.AddAmount(self.value)
    } else {
        receiver = self.Receiver()

        // Subtract the amount from the senders account
        sender.SubAmount(self.value)
        // Add the amount to receivers account which should conclude this transaction
        receiver.AddAmount(self.value)

        snapshot = self.state.Copy()
    }

    msg := self.state.Manifest().AddMessage(&ethstate.Message{
        To: receiver.Address(), From: sender.Address(),
        Input:  self.tx.Data,
        Origin: sender.Address(),
        Block:  self.block.Hash(), Timestamp: self.block.Time, Coinbase: self.block.Coinbase, Number: self.block.Number,
        Value: self.value,
    })

    // Process the init code and create 'valid' contract
    if IsContractAddr(self.receiver) {
        // Evaluate the initialization script
        // and use the return value as the
        // script section for the state object.
        self.data = nil

        code, evmerr := self.Eval(msg, receiver.Init(), receiver)
        if evmerr != nil {
            self.state.Set(snapshot)

            statelogger.Debugf("Error during init execution %v", evmerr)
        }

        receiver.Code = code
        msg.Output = code
    } else {
        if len(receiver.Code) > 0 {
            ret, evmerr := self.Eval(msg, receiver.Code, receiver)
            if evmerr != nil {
                self.state.Set(snapshot)

                statelogger.Debugf("Error during code execution %v", evmerr)
            }

            msg.Output = ret
        } else {
            // Add default LOG. Default = big(sender.addr) + 1
            addr := ethutil.BigD(sender.Address())
            tx.addLog(vm.Log{sender.Address(), [][]byte{addr.Add(addr, ethutil.Big1).Bytes()}, nil})
        }
    }

    return
}

func (self *StateTransition) Eval(msg *ethstate.Message, script []byte, context *ethstate.StateObject) (ret []byte, err error) {
    var (
        transactor    = self.Sender()
        state         = self.state
        env           = NewEnv(state, self.tx, self.block)
        callerClosure = vm.NewClosure(msg, transactor, context, script, self.gas, self.gasPrice)
    )

    evm := vm.New(env, vm.DebugVmTy)
    ret, _, err = callerClosure.Call(evm, self.tx.Data)

    return
}

// Converts an transaction in to a state object
func MakeContract(tx *Transaction, state *ethstate.State) *ethstate.StateObject {
    addr := tx.CreationAddress(state)

    contract := state.GetOrNewStateObject(addr)
    contract.InitCode = tx.Data

    return contract
}